The practice of orthodontics involves the correction of dental irregularities and malocclusions by the application of forces to the teeth. The orthodontist applies corrective forces to the teeth requiring repositioning by attaching orthodontic appliances to them. These appliances are then connected to each other by an archwire made of a spring-like metal e.g., stainless steel. The orthodontist controls the amount and direction of the forces required to effect a repositioning of the teeth by selective bending of the archwire. This invention is directed to a more selective and precise method of applying such corrective forces and an appliance system designed to implement this improved treatment method.
Current standard orthodontic treatment methods employing fixed orthodontic appliances can for the most part be divided into two broad categories i.e., the light wire method and rectangular wire (or edgewise) method. Each of these methods has its advantages and its disadvantages. The improved orthodontic appliance system of this invention allows the practitioner to utilize the advantages of both and to avoid the disadvantages inherent in each method.
The light wire method involves effecting tooth movement by tipping and torquing the tooth into a new position. In the light wire method, an appliance, attached to a tooth, is connected to an archwire at what can be described as a point contact. Corrective force is applied to the tooth through the archwire, but because of the point contact connection between the archwire and the tooth, it is free to rotate and tip. This rather loose connection allows the tooth to move easily and large changes in tooth position can be accomplished by the use of light forces. However, since the tooth is relatively free to move, it is difficult to precisely control its final position.
The rectangular wire method uses a more rigid system to effect tooth movement. A rectangular archwire is positioned in a rectangular slot in an appliance that has been attached to a tooth. The degree of freedom of the tooth to move in any direction is limited because of the rigid connection formed by the rectangular archwire in the rectangular archwire receiving slot. A tooth so attached must move along or with the archwire and precise repositioning is possible. However, since the connection between the appliance and the archwire is rigid and extensive, large frictional forces are encountered and therefore higher forces must be used to accomplish a particular tooth movement. Generally a longer treatment time is required to effect large tooth movement by this method than by the light wire method.
Various attempts have been made in the past to design orthodontic appliances that are capable of being utilized to effect both methods of treatment. U.S. Pat. Nos. 3,163,933 and 3,178,822 describe combination one-piece orthodontic appliances having the capability of being used in either the light wire or rectangular wire method. These devices have enjoyed limited success perhaps because of their design or lack of flexibility.
U.S. Pat. No. 3,128,553 describes an orthodontic appliance with an interchangeable element that permits the orthodontist to eliminate some of the control problems inherent in the light wire treatment method. The appliance in a first configuration is a standard light wire unit. As treatment progresses, an auxiliary element having laterally projecting wing portions is insertable in the appliance and the tendency for the tooth to rotate about its vertical (gingival-occlusal) axis is reduced by the extending wings.
Various other attempts have been made in the past to provide a less empirical approach to orthodontic treatment which is in part an art centering about the orthodontist's skill and speed in constructing arch-wires with the proper force-producing bends. One such attempt is the so called straight-wire technique. This is a modified rectangular wire system wherein the orthodontist first makes a model of the patient's dental arch. Then using this model, he selects certain rectangular wire appliances having what he considers to be the proper amounts of torque and/or angulation to effect the repositioning of the teeth. Still using the model of the patient's dental arch, he welds the selected appliances on bands at predetermined positions based on his study of the model. These bands are then positioned on the model, an archwire is constructed with predetermined bends and then the whole assembly is transferred to the patient's teeth.
U.S. Pat. No. 2,908,974 describes a rectangular wire appliance in which the archwire is attached to a tooth by means of a two-piece unit having a female member attached to the tooth and detachable male member having an archwire receiving slot. The male member of this device can be constructed with different degrees of angulation or torque and they can be changed as treatment progresses to effect positioning of the teeth with minimal wire bending. This device does not have the capability of being used in the light wire treatment method and its design makes it difficult to effect a rigid connection between the female member and the male member.
Although the straight wire treatment method can be considered a more precise method than the conventional rectangular wire system, it is time consuming and it is not easily modified. One skilled in the art will readily appreciate the advantages of my invention hereinafter described since it provides all the advantages of the rectangular wire or straight wire methods with the increased capability for quick modification as treatment progresses, and the advantage of light wire treatment capability.
Another not so apparent advantage of my invention is that it provides a practical and safe means for an orthodontist trained in the light wire treatment method to practice the rectangular wire method without radically diverting from his primary skill; the converse, of course, being applicable to one having his basic training in rectangular wire treatment method.